I was surprised to see this in the public Goblin Line timetable. It's
shown as an MF service calling all stations from Woodgrange Park to
Upper Holloway, which is marked with an a for arrival time. The column
has a C code which means it continues to Willesden junction Low Level.
Table 59 does not show this train between Gospel Oak and Willesden.

Does this train actually run to Willesden, and can passengers stay on board?